Call distributing telephone system



June 21, 1938. 1?'. B. BLAKE CALL n'isTaIBuTING TELEPHONE SYSTEM Filed July 27, 1937 14 Sheets-Sheet l NNN) www1@ ITL N ...YM

June 21, 1938. B BLAKE 2,121,419

CALL DISTRIBUTING TELEPHONE SYSTEM Filed July 27, 1957 14 Sheets-Sheet 2 /N VE N 70%? By E@ mmf@ June 21, 1938. F. B. BLAKE v 2,121,419

CALL DISTRIBUTING TELEPHONE SYSTEM FiledJuly 27, 1937 14 Sheets-Sheet 3 /N VE N TOR 11; f.` BLA/f5 By@ 6. M

ATTORNEY Junezl, 193s. I P BBLAKE 2,121,419/

CALL DISTRIBUTING TELEPHONE SYSTEM IIIIIIIIIIHIIIIH /N VEA/TOR E BLA/(E Y Byamze A TTOR/VEV F. B. BLAKE CALL DISTRIBUTING TELEPHONE SYSTEM Filed July 27, 1937 June 21, 1938.

14 Sheets-Sheet 5 /NVENTOR F BLAKE' By@ '6. M

A TTOR/VE y June 21, 1938. F. B. BLAKE CALL DISTRIBUTING TELEPHONE SYSTEM Filed July 27, 1937 14 Sheets-Sheet 6 /NVENTOR .E B. BLAKE A 7' TOR/VE? JuneZl, 1938. F. BBLAKE Y CALL` DISTRIBUTING TELEPHONE SYSTEM Filed July 27, 1937 14 Sheets-Sheet 7 INI/ENTOR. n E BLA/E @w June 2l, 1938. F B BLAKE i cALL DISTRIBUTING TELEPHONE SYSTEM Filed July 2'7, 1957 14 Sheets-Sheet 8 /A/l/ENTOR B. BLAKE ATTORNEY June 2l, 1938. 1.-, B BLAKE l 2,121,419

CALL DISTRIBUIING TELEPHONE SYSTEM Filed July 27, 1937 14 Sheets-Sheet 9 S n S A TTORNEV June 2l, 1938. F. B. BLAKE CALL DISTRIBUTING TELEPHONE SYVSTEM Filed July 27, 1937 14 vSh'ees--Slgeevl'I l0 /NVE/VTOR f.' B. BLA/(E 6'? M ATTORNEY June 2l,y 1938. F. B. BLAKE 2,121,419

CALL DISTRIBUTING TELEPHONE SYSTEM I Filed July 27, 1937 14 Sheets-Sheet 11 ATTORNEY June 21, 1938.

F. B. BLAKE CALL DISTRIBUTING TELEPHONE SYSTEM Filed July 27, 1937 14 Sheets-Sheet l2 Q .wi

/NVENTOR E BLAKE @csw'w ATTORNEY June 21, 1938.

CALL DISTRIBUTING TELEPHONE SYSTEM Filed July 27, V193'? 14 Sheets-Sheet 13 ATT'oR/VEV June 2l, 1938. F. B. BLAKE CAVLL DISTRIBUTING TELEPHONE SYSTEM FlAed July 27, 1937 14Y Sheets-Sheet 14 QQQ /A/VENTOR v' B. BLA/(E 6'? 6. imid- ATTORNEY Patented June 21, 19,38

UNITED STATES CALL ms'rRIU'r-ING TELEPHONE SYSTEM Foster B. Blake, Mountain View, N.J., assgnor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application July 27, 1937, Serial No. 155,873

Claims.

This application relates to telephone systems and has for its object to increase the efliciency of such systems.

In systems of the type disclosed in lPatent 5v 1,517,260 granted to F. A. Stearn, December 2,

1924, calls originating in a manual oilice for completion in a full mechanical oiice are handled at the terminating oce by an operator known as the B operator. A plurality of trunks appearat 30, each B operators position in listening keys and corresponding lamps. A call incoming on one of these trunks lights the associated lamp and the B operator connects her headset with that of the originating operator by depressing the listening key individual to the trunk.

The efficiency of this system is greatly improved by distributing the calls on a straightforward basis to operators positions common to all trunks. 'I'his increases the eiilciency of the switchboard 2Q, since it tends to distribute evenly the incoming calls over the occupied positions resulting in economical operation during the most busy periods.

More specically, the incoming trunks, arranged in groups, are served by a corresponding AA group of link circuits which in turn are served by a common position finder circuit. As calls reach trunks in the group, an allotted idle link circuit connects with the calling trunk and then appropriates the position finder circuit for its individual use.

Furthermore, if a second call is received in the group while the first call is being served, a second link circuit will be allotted, will hunt for and connect with the second calling trunk and will then wait until the position finder circuit is freed by the first link. When the position nder circuit is released, the presence of the second calls holds the position finder switch in its last used position and prevents the release of the operators position.

In this arrangement if the number of operators available is less than the number of trunk groups and calls arrive with overlapping frequency it might be possible that calls in certain groups would be greatly delayed. To prevent this, an arrangement is provided in accordance with the present invention whereby, if all operators remain busy for a predetermined length of time, the position iinder is automatically stepped forward when an operator has completed her handling of a call thereby freeing her position for selection by some other group of trunks.

` This and other features of the present invention will be more clearly understood from a consideration of the following description in connection with the drawings in which:

Fig. 1 shows the manner in which Figs. 3 to 15 should be arranged to disclose the invention;

Fig. 2 is a diagrammatic showing of the circuits serving one trunk group; and

Figs. 3 to 15 show enough detailed circuits for a clear understanding of the invention, Fig. 3 showing an incoming selector, Figs. 4 and 5 Showing one link circuit, Fig. 6 showing the position nder control circuit, Fig. '1 showing certain timing and alarm circuits associated with the link circuit, Fig. 8 showing the position lnder and key-set selector, Fig. 9 showing the operators position circuit, Fig. 10 showing the calls waiting alarm circuit, Figs. 11 and 12 showing the allotter circuit, Fig. 13 showing one operators key-set and Figs. 14 and 15 showing the key control circuit.

Referring rst to Fig. 2 a group of one hundred trunks, 200, 201, etc. terminating in incoming selector circuits 202, 203, etc. and incoming selector switches 204 are served by a pair of allotter circuits 205 and 206 and by link circuits 201 to 2| 1. With both allotters in service the allotter 206 allots links 209, 210, 211 which are located on the front of the link frame while allotter 205 allots links 201 and 208 on the rear of the frame. Each link has access to the one hundred trunks of the group over the trunk finder bank 212 and to one hundred senders over the sender selector bank 213. The five links 201 to 211 are connected in multiple over the transfer switch 214 to a position nder circuit. Normally, they are connected to position finder circuit 215 which in turn controls two switches 216 and 211, switch 211 havingaccess to the operators position circuit 218 and switch 216 having access to the key control circuit 219. An emergency position finder circuit 220 is provided which may be substituted for the regular position finder by means of transfer switch 214. Other groups of links are indicated which also have access to the operators position through their position iinders. The operators position may also be seized by a sender test frame 221. cess to called subscribers lines such as line 222 through final selector frames, such as frame 223.

Briefly the operation is as follows: A call incoming on a trunk such as trunk 200 Vcauses a preallotted link, for example link 201, to hunt for the trunk and to simultaneously hunt for an idle operators position. When the position is found, the key control finder is advanced to the corresponding position. The B operators posi- The incoming selectors have action is then connected through to the originating operators position and the wanted number is transmitted, while at the same time the link hunts for an idle sender. As soon as the wanted number is received the E operator operates her keyset and is then disconnected from the link. When an idle sender is found the key-set is connected thereto and the number recorded in the sender. The key-set is then released, and under the control of the sender, the incoming and final selectors are operated to complete the connection with the called line after which the sender and link circuit may restore to normal.

Before describing the detailed operation of the circuits shown in Figs. 3 to 15 certain features of the equipment will bejdiscussed. As mentioned above, two allotters are provided for the link group and they are used alternatelyone normally allotting the three links on thefront of the frame in succession after which the other allotter successively allots the twoy links on the rear of the frame. However, either allotter may be removed from service and the otherl allotter made to assign all links. To this end each allotter is equipped with vthree jacks, for example, the allotter of Fig. 12`is provided with jacks |204, |205 and |205, while the allotter of Fig. l1 is provided with jacks |||2 and |||3. A double plug |201 connects jack |206 with jack |208 connected with the two rear links, while the double plug.|||4 connects jack |||3 with the jack |||5 extending to the three fro-nt links. Under normal conditions the plug |203 is inserted in the jack |204 and the plug is Yinserted in the jack but if either allotter is to be removed from service, for example the allotter of Fig. 12, plug |203 will be removed from jack |204 and inserted in the jack |205. Similarly if the allotter of Fig. l1 is to be removed from service plug |||0 will be removed from jack and inserted in jack |||2. Similar multicontact plug and jack connections are used between the key control selector and the key control circuitand also between the key-set and the key control circuit. In general, these plug and jack connections will be omitted in tracing the circuits hereinafter. l

The sender indicated at 550 in Fig.` differs from that shown in the patent to Stearn above referred to only in that the battery and ground supply to the registration circuits is reversed between digits to minimize contact injury.

Referring now to Figs. 3 to 15, inclusive', the link circuit of Figs. 4 and 5 when idle 'and not allotted stands with its sequence switch 500 in position H. The connection shown between this link and the allotter of Fig. ll identiiies it as the iirst link on the front of the link frame. When the last link on the rear of the frame has connected with an operators position it ccnnects ground to conductor |2||, advancing sequence switch |200 of the rear allotter to position l. Sequence switch H00 of the frontallotter has been standing in position 8, therefore the advance-of switch. |200 Yto position closes a circuit from ground over the lower right and upper left contacts of cam |2|2, through-jack |204 and plug |203, upper right contact' of 'cam H02 to the-winding of sequence switch magnet H00 and battery, advancing the sequence switch to position 0. It is at once advanced to position I0 in Ya circuit extending Yfrom battery through the winding of sequence switch magnet H00, lower right Contact of cam I6, conductor which extends in multiple to all lve link circuits and may be traced in the link circuit shown over the inner upper normal contact of key 400, to ground over the lower left contact of cam 509 and the lower right contact of cam 504. When sequence switch ||00 reaches position |0 a circuit is closed from battery through the winding o-f sequence switch magnet |200, upper right `contact of cam |2|3, through jack and plug |||0, upper left and lower right contacts of cam |||8 to ground at the inner lower back contact of relay H05. Sequence switch |200 is advanced to its waiting position, position 8, by this circuit.

With sequence switch ||00 in position I0 (or position it closes a circuit from ground at the upper back contact of relay ||05, plug |203 and jack |204, upper contacts of cam |200, jack |204 and plug |203, upper contacts of cam ||04 to conductor ||20 individual to the link of Figs. 4 and 5, which extends over the middle lower normal contact of key 400, lower right contact of cam 500 and cam 545 of sequence switch 500, auxiliary contact of jack 406 in. parallel with the lower back Vcontact'of relay 4| 4, winding of magnet 500 to battery. Sequence switch 500 advances to position by this circuit, in which position the link is ready for use on an incoming call.

It may be noted that the contact of jack 406 and the contact of relay 4|4 are included in the circuit of sequence switch magnet 500 for a purpose to be explained later. Since these contacts appear in each circuit, they will, for brevity, be omitted from the circuits for magnet 500 to be'traced hereinafter.

Assuming that the incoming selector circuit of Fig. 3` is seized at the originating office, a circuit is closed from battery in Vthat oflice over the ring conductor 30|, upper left winding of repeating coil 303, through the upper and lower windings of relay 304 in series, lower left winding of repeating coil 303, tip conductor 305 and thence to ground at the originating oilice. Relay 304 operates in this circuit. If no other call is waiting for service, so that relay '|00 is unoperated, relay 304 closes a circuit from battery through the winding of relay 306, front contact of relay 304, right contacts of sequence switch cam 3|3 to conductor 301 and thence to ground at the upper back contact of relay 100. Relay 306 in operating opens one connection to the group busy circuit and prepares circuits to be used hereinafter. Relay 304 closes a circuit, in parallel with the winding of relay 305, from battery through the upper winding of relay 308, lower right contact of cam 309, lower left contact of cam 3|0, front contact of relay 304 and thence to ground as previously traced. Relay 308, in operating, closes a circuit from battery through the winding of sequence switch magnet 300, upper right contact of cam 3| lower front contact of relay 308 to ground over the lower contacts of cam 3|2. Sequence switch 300 advances to position 2 by this circuit. When the sequence switch reaches position |3A a locking circuit for relay 305 under the control of relay 304 is closed,

which may be traced from battery through the oirelaryy 305, front contact of relay 300, upper contacts of cam 3|3 to ground at the front contact of relay 306.

When sequence switch 300 reaches position 2 ground is connected over the lower contacts of cam 3|4 to start conductor 3I5 leading to the link allotter circuit where it extends over the contact of key 10|, to conductor 150' and over the` auxiliary contact of jack 102 to the winding of relay 100 and battery. Relay 100, which is common to the group of incoming selectors, operates in this circuit opening the operating circuit for relay 306 and removing ground from similar circuits to other selectors. Relay 100, therefore, prevents any subsequent calls on trunks of the trunk group from advancing their incoming selector sequence switches to the start position until such time as all selectors which advanced before its operation have been served.

The operating circuit of relay 308 is opened in position 2 of sequence switch 305 and therefore relay 308 now releases. With relay 308 released, ground is removed from conductor 3|6, to mark this selector as calling. l y

The ground connected to conductor 150 is also applied over the lower back contact of relay |05, to conductor |119. This conductor is connected in` multiple to all or the link circuits but'since sequence switch 500 is the only switch standing in position l, being the one allotted for use, a crcuit will be completed over the lower normal contact of key 400, lower contacts of sequence switch cam 40|, winding of relay 50| and battery. Relay 50| operates and closes a circuit from battery through the upper winding of relay 404, lower contacts of cam 405, outer right front contact of relay 50| to ground over the right contacts of cam 505. Relay 464 operates and in turn closes a circuit, from battery through the winding of sequence switch magnet 500, upper contacts of cam 505 to ground at the upper front contact of relay 404, advancing sequence switch 550 into position 2. With"sequence switch 506 in position 2, a circuit is closed from batterythrough the winding of up drive magnet 4 l 0 of the trunk nder 4,50, upper left and lower right contacts of cam 465, outer right front contact of relay 50| to ground over the right contacts of cam 504, advancing the line iinder in search of the incoming trunk of Fig. 3 which has been marked by the removal of ground from conductor 356. Relay 50| is held operated over its inner right front contact, lower contacts of cam 502, commutator strip 451 andbrush 442 to ground between sets of terminals and over the upper contacts of cam 503,- normal contact of relay 402, brush 403 and the upper contacts oi cams like cam 3|1 to ground as it passes trunks which are not in calling condition.

When the calling trunk of Fig. 3 is found and the brushes of trunk nder 450 are centered, relay 50! releases opening the circuit of the up drive magnet M0, and bringing the trunk finder to rest. The release of relay 50| also connects ground over its right back contact to brush 403 to mark the incoming selector as busy. In addition it closes a circuit from battery through the winding of relay 1108, upper right and lower left contacts of cam i139 to ground at the left back contact of relay 50|. The operation of relay 408 also closes an obvious circuit for relay 4| 2.

The advance of sequence switch 500 from position l opens the operating circuit of relay 404 and that relay releases. With relay 404 released a circuit is closed from battery through the winding of sequence switch .magnet 500, upper right contact oi cam 506 to ground at the upper back contact of relay 404, advancing sequence switch 500 to position. 3, in which it-remains until the trunk is found as indicated by the operation of relay 408. The operation of relay 408 closes a circuit from ground over its outer lower front contact, upper left contact of cam 501, to the winding of sequence switch magnet 500 and battery, advancing the sequence switch to position 4.

With relay 4|2 operated and sequence switch 500 in position 4, a circuit is closed from battery through the winding of relay 500, in the position nder circuit lower back contact of relay 60|, contact 508 of transfer switch 596, upperl contacts of cam 4| l, outer lower contact of relay 4| 2, trunk finder brush 4|3, conductor 36|, left contacts of cam 3|3, upper front contact of relay 306 to ground. Relay 600 operates and closes a holding circuit for itself through the winding of relay 66| over the lower front contact of relay 600, switch contact 546, inner lower back contact oi relay M4, upper left contact of cam 509 and Vlower' right contact of cam 504 to ground. Re-

lay 60| does not operate in this circuit being shunted by the operating circuit of relay 600. Relay 600 closes a circuit from ground over the upper back contact of relay M4, upper right and lower left contacts of cam 4|5, upper back contact of relay 402, switch contact 5|0, conductor 606, back contact of relay 60|, inner upperfront con-- tact of relay 600, switch contact 5| l, upper right and lower left contacts of cam 512, outer upper contact of relay 4|2, brush M6, conductor 320, upper right contact of cam 32| to the winding of sequence switch magnet 360 and battery, advancing switch 300 to position 3. The advance of sequence switch 300 from position 2 releases relay 100, restoring ground to conductor 361 and permitting other incoming selectors to advance to the calling position.

The advance of sequence switch 555 to position 2 as previously described seizes the position finder circuit, if free, by connecting ground to conductor S09 thereby closing a circuit from ground over the back contact of relay M5, upper right and lower left contacts of cam M5, upper back contact of relay 402, transfer switch contact 5w, conductor 609, lower back contact of relay 654, upper back contact of relay 665, upper normal contact of relay 656, lower back contact of relay 601 to the winding of relay 658 and battery. Relay 608 operates and closes a circuit from battery through the winding of relay 5m, outer lower back contact of relay 6H, outer upper front contact of relay 605, upper back contact of relay 6|2, to conductor 669 and thence as previously traced to ground. Relay 608 also prepares the double test relay 601 for testing for an idle operators position. It closes a circuit from, battery through the lower winding of relay 601, inner upper front contact of relay 660, upper winding of relay 601, inner lower back contact of relay 602 and ground to prepare the relay for operation. A branch of this circuit eX- tends from ground through the upper and middle windings of relay 601, inner lower iront contact of relay 6|!) to brush 605 of position iinder S00. Relays 603 and 5m close a` circuit for relay 6|3 which may be traced from battery through the winding of that relay over'the back contact of stepping magnet 801, lower back contact of all-positions-busy relay 6M, upper front contact of relay 6|0, lower front contact of relay 608 to ground at the upper back contact or relay 661. Relay 6|3 in turn operates and closes a circuit from battery through the winding of stepping magnet 851, lower front contact of relay 6|3, lower back contact of relay 5M and thence as traced for the circuit of relay 613 to ground at the back contact of relay 651. Magnet 851 in operating opens the previously traced circuit of relay 6|3 which in releasing opens the circuit of magnet 801 and this magnet and relay cooperate until an idle operators position is found.

Such a position is indicated by the presence of battery on a terminal to which brush 804 has access, which is brought about as follows: When an operator occupies her position, she inserts the plugs of her headset, made up of transmitter 900 and receiver 90|, into telephone jacks 902 and 903 thereby closing a circuit from ground through the right winding of repeating coil 904, tip contact of jack 903, transmitter 900, tip contact of jack 902, winding of relay 905 to battery. Relay 005 operates and in turn closes an obvious circuit for relay 906 which operates and extends battery through resistance 909 over its upper front contact and the outer lower back contact of relay 901 to conductor 908 to mark the position occupied. Conductor 908 terminates in the arc served by brush 804 of position nder 800, thereby completing the test circuit through the middle winding 601 which now operates.

Relay 601 in operating opens the circuit of both relay 6I3 and magnet B01, bringing the position finder 800 to rest. Relay 601 closes a locking circuit for itself from battery in the operators position as traced through brush 804, inner lower front contact of relay 6I0, middle winding of relay 601 to ground at the upper front contact oi' relay 601. The operation of relay 601 also opens the operating circuit of relay 608 which now releases, and when it closes its lower back contact completes a circuit from battery through the winding of relay 606, lower back contact of relay 608, lower front contact of relay 601, normal contact of relay 606, upper back contact of relay 605, lower back contact of relay 604 to grounded conductor 609. Relay 606 locks over its upper alternate contact to conductor 609 over a part of its operating circuit independent of relays 608 and 601. With relay 606 operated, grounded conductor 609 is extended over the lower front contact of relay 6|0, lower front Contact of relay 606, winding of relay 6| I, brush 803 of the position finder, lower back contact of relay 9| 0 or inner lower front contact of relay 906 to the winding of relay 901 and battery. Relay 901 operates in this circuit disconnecting battery from conductor 908 to mark the position busy, lights lamp 925 to warn the operator of an incoming call and disconnects Vground from conductors 852 and 853 leading to the positions busy circuit.

Relay 6|| also operates in this circuit, locking over its inner lower front contact, the upper back contact of relay 6| 3 to grounded conductor 609. Relay 6|I closes a circuit from battery through the winding of relay 605, inner upper front contact of relay 6| I, inner upper back contact of relay 604 to conductor 609. Relay 605 operates, opening the locking circuit of relay 606 and that relay releases. Relay 6|| in operating also closes an obvious circuit for relay 602.

With relay 602 operated, ground is connected to brush 80| of the position finder, and through a terminal engaged by that brush to a corresponding'terminal accessible to brush 8|6 belonging to the key-set finder 8I0 to which the winding of relay 6|5 is connected. Relay 602 also closes a circuit from ground at its outer lower front contact,lower back contact of relay 6 I 1,back contact of relay 6I5, if the key control circuit has completed its operation on the last previous call, back contact of stepping magnet 8I1 of the keyset finder, winding of relay @I6 and battery. As ln the case of relay 6|3, relay 6|6 operates and closes a circuit for the corresponding stepping magnet 8I1 which extends from battery through the winding of magnet 8| 1, upper contacts of relay 6|6, lower back contact of relay 6|5 and thence over the operating circuit of relay 6|6. Relay 6|6 and magnet 8|1 cooperate as in the case of relay 6|3 and magnet 801 to advance the key-set nder 8| 0 until brush BIG engages the terminal marked by position nder 800 at which time the circuit of relay SI is closed and that relay operates, opening the circuit of relay 6|6 and magnet 8| 1 and stopping the advance of the key-set nder 8I0.

The advance of sequence switch 300 from position 2 opens the operating circuit of relay 600 and permits relay 60| to operate in the locking circuit of relay 600. Relay 60| further opens the operating circuit of relay 600. It also closes ground on the outer lower back contact of relay 602 over the inner upper front contact of relay 60| to conductor 603 leading to the calls waiting signal circuit which will be described hereinafter. The operation of relay 602 in response to the engagement of the operators position removes this ground from conductor 603.

With relays 600, 60| and 605 operated a signal is transmitted to the incoming trunk to connect the A and B positions together. A circuit is closed from battery through resistance 6 9, lower back contact of relay 618, lowe1` front contact of relay 605, outer upper front contact of relay 60|, inner upper front contact of relay 600, contact 5|I, upper right and lower left contacts of cam 5|2, upper front contact of relay 4|2, brush M6, conductor 320, winding of relay 322, lower left and upper right contacts of cam 359, upper back contact of relay 302, left contacts of cam SI2 to ground. Relay 322 operates in this circuit, connecting the tip and ring conductors of the trunk circuit over conductors 325 and 324, switch contacts 5|6 and 5|5 of switch 590 to condensers 620 and 62| and thence over the upper front contacts of relay 602, brushes 805 and 806 of the position nder, to the terminals of choke coil 9i I, the armatures of relay 9I3 and over the back contacts thereof to the secondary winding of tone coil 92|. Relay 322 also closes a circuit from ground over its outer lower front contact, conductor 323, switch contact 5|4, inner upper front contact of relay 602, brush 002, winding of relay 9I0 and battery.

Relay 9|0 in operating initiates the operations which result in the transmission of two zip tones to the A operator and the connection of the two operators headsets in talking relation. Relay 9|0 closes a circuit from ground over its outer upper front Contact, normal contact of relay 9|4, resistance SI5, winding of relay SEG and battery. Relay 9|6 operates and closes a circuit from the tone source through the primary winding of tone coil 92|, lower normal contact of relay 9|1 to ground the lower front contact of relay 9|6. At the same time it closes a circuit from ground over its upper front contact, upper back contact of relay 9|3, winding of relay SI1 to battery. The closure of the primary circuit of tone coil 92| transmits an impulse of tone current to the originating operators position over the talking conductors as previously traced and thence through the repeating coil 303 out over tip and ring conductors 305 and 30 I, respectively. The operation of relay 9|1 opens the primary circuit of the tone coil thereby terminating the rst tone impulse. Relay 9|1 extends its operating ground to the Winding of relay 9|8 which operates after an interval to reclose the primary circuit of tone coil 92| and to extend the operating groun-d of relay 9|1 to the winding of relay 920. Relay 920 after an interval closes a circuit for relay 9|3 which disconnects the secondary of the tone coil from the talking conductors thereby terminating the second impulse of tone. Relay 9|3 also locks over its inner upper contact to ground at the upper iront contact of relay 9|9. With relay 9| 3 operated the talking circuit extends over the outer upper front contact of relay 9|3, normal contacts of key 922, ring of jack 993, the operators headset receiver 90|, ring of jack 902 and the lower front contact of relay 953 thereby permitting the A operator to transmit the wanted number to the B operator. The tones transmitted to the A operator are also heard by the B operator through condensers 923 'and924 preparing her to receive the wanted number.

As soon as the number has been 'passed the B operator writes'it up on her key-set shown in Fig. 13. Assuming thatV the wanted number is 2193 she will depress key |302 in the thousands row, key |3|1 in the hundreds row, |329 in the tens row and |333 in the units row, When the rst key `is operated, a circuit is closed from ground Ythrough the `winding of relay |400, through the windings of the release magnets |35 |352, |353 and |3541in parallel, right contact of key |302, contacts'of sequence switchcam |502, winding of relay |503, resistance |504 and battery. ,None of these release magnetsandrelays operate in this circuit, there being insuiicient current to operate relay |400 or any of the release magnets and relay |503 being 'shunted by a i circuit extending from battery through resistance |504, over the back contact of relay |503 and in parallel over thenormal contacts |34|, |342, |343 and |344 of each of the key strips until'a key in each of the strips has been operated. When this occurs, the shunt is removed fromrelay |503 and that relay operates, closing a circuit from ground over its upper ironticontact, left contacts of cam |505,-upper back contactofrelay |493, lower right and upper left contacts of cam |50i, `conductor 333, brush 8|3 of switch 3|9, upper front contact of relay 5|5, lowerback Contact of relay SI1, to the lower winding `of relay SIB and battery, Relay 9|9 operates `in this" circuit, opening the' operatingcircuit of `relay322 which in turn releases relay 9|0. Relay 9|0 opens the holding circuit of relays 9`|6 and 9|3, restoring the tone relays andthe operators talking circuit to normal. u U

In the meantime the operation of relay 505 followingthe connection with the operators position circuit started' the hunt for a'n i-dle sender Vby completing a circuit from grounded conductor 509 over the lower back contact of relay 004, upper front contact of relay 005, lower front contact of relay 69|, switch contact 5|3, lower back contact of relay 103, lower back contact of relay 402, upper contacts of cam 40|, upper winding of relay 404 to battery.` Relay 494 operates and closes a circuit from ground over its'upper front contact, upper contacts of cam 595, to the winding of sequence switch magnet 500 and battery advancing the sequence switch to Vposition 5. The advance of sequence switch 500 is signaled to the position finder circuit by la circuit extending from the upper back contact of relay 4|4, upper contacts of cam 4|5, switch contact 534, winding of relay 904 an-d battery. Relay 504 operates, opens the locking circuit of relay 505 and prepares a locking circuitV for relayV 6|8.

With sequenceswitch 500 in position' relay 494 closes a circuit from ground over its upper front contact, upper left and lower right contacts of cam 505, throughthe winding of the up drive magnet 5|1 of sender nder 520 for advancing the nder in search of an idle sender. In position 5 the operating circuit of relay 494 is opened, but this relay remains operated in a circuit through its lower winding, upper left and lower right contacts of cam 4|l' to the centering commutator strip 5|8, brush 541 'and ground. It also is held operated in a circuit from battery through its upper winding, upper contacts of cam 4|8, lower front contact oi relay 404, upper. right and lower left contacts of cam 4|9 and finder brush 52| as it passes over busy senders. When an idle sender is found and the brushes are Vproperly centered, both hol-ding circuits for relay 494 are opened and that relay releases and closes a circuit from ground over its upper back contact, upper right contactof cam 503,110 the winding of sequence switch 500 and battery,` advancing the sequence switch to position 9.

With relay |8 operated to indicate that the number has beenV completely set up `on the keyset and sequence switch 500 in position 6L to indicate that 4an idle sender has been found, a circuit is closed from battery through the upper winding of relay |403, left contacts of cam |404, conductor 332, brushl 8|2, upper front contact of relay |8, switch Contact 522, right contacts oi'cam 523, winding of relay 429, outer upper normal contact of key 400 to ground at the inner lower contact of relay 4|2. Relay`|403 operates and locks to its operating circuit through its upper winding and inner upper front contact and the upper contacts of cam |404. With relay |403 operated, sequence switch |590 is advanced from position i in a circuit from battery, through the winding of magnet |500', lower left Contact of cam |509, outer upper front contact of relay |403 to ground over the left contacts of cam |505 and the upper front contact of relay |503. AtV

relay 404, lower left and upper right contacts of cam 405 to ground at the innermost front contact of relay 420. Relay 404 operates and closes a circuit from ground over its upper front contactupper contacts of cam 505 to the winding of sequence switch magnet 590, advancing the sequence switch to position 1. When sequence switch 509 leaves position 5 it disconnects ground from conductor 909, thereby releasing relays 6|8, 9|| and 901 and freeing the operators position unless another call is waiting in the group. Relay 420 also closes a circuit from ground at itssecond lower front contact over switch contact 524 to the winding of relay 5H and battery. In addition relay 420 prepares the Asender recording circuits by connecting brush 525 of the sender finder over the outer lower front contact of relay 420, switch contact 529, key-set finder brush 854, conductor 834, upper right contact of cam to cam |405; brush 521 of the sender finder over the upper Vfront contact of relay 420, switch contact 520, key-set finder brush 0| conductor 03|, upper left contact of cam |501 to cam |409. Furthermore, with sequence switch 500 in position 'i brush 529 is connected over the lower right and upper left contacts of cam 42 lower irontcontact of relay 404, upper left and lower right contacts of cam 4|8, switch Contact 530, key-set finder brush 3|5, conductor 835, to cam |401.

Registration in the sender is controlled by certain circuit conditions set up on these circuits Vas determined by the operated keys of the key-set of Fig. 13. As the sequence switch 500 passes through positions 2, 3, 4, and battery and ground through various resistances are connected to these circuits. 'Ihe register relays of the sender which are not shown are marginal and non-marginal, the marginal relays responding to low resistance conditions, while the non-marginal relays operate under all conditions. The

' sender and its operation is disclosed in the aboveidentified patent to Stearn. Assuming as before that keys |302, |3|1, |329 and |333 are operated with sequence switch |500 in position 2, the thousands digit is transmitted to the sender. The circuit extending to cam |406, which will be called circuit A, extends in two branches, one over the lower right contact of cam |406, through both of windings of relay |408 to ground at the back contact of relay |508. The other branch of this circuit extends over the upper left contact of cam |406, inner right contact of key |302, upper contacts of caniY |409 to the lower winding of relay |408, thereby shunting the high resistance upper winding of that relay and creating a low resistance ground condition on circuit A. Relay |408 operates in this circuit and locks to ground at its own upper front contact. The circuit closed to cam |405, which will be ldentifled hereinafter as circuit B, extends over the lower left contact of that cam to the left con'I tact of key |302, resistance |4|9, right contacts of'carn l|4| 1, resistance I4 |8 to battery creating a high resistance battery condition on circuit B. With relay |408 operated the circuit closed through cam |401, which will be identied as circuit C, is extended over the upper right and lower left contacts of cam |401, resistance 4| 2, upper front contact of relay |408, resistance |4|0, lower right and upper left contacts of carn |4|| to battery, producing a high resistance battery condition on circuit C.

Relay |408 also closes a circuit from ground over its inner upper front contact through the winding of relay |508, right contacts of cam |509 to battery. When relay |408 starts to operate relay |508 is shunted by a circuit over the right contacts of cam |509, upper back contact of relay |508 to ground at the upper normal contact of relay |408 but this circuit is immediately opened, permitting relay |508 to operate and open the operating circuit of relay 408. the registration of the thousands digit has been accomplished at the sender, all three registration circuits are opened and relay |403 releases, connecting ground over its normal contact and the upper front contact of relay |508, lower right contact of cam |5||) to the winding of sequence switch magnet |500 and battery, advancing the sequence switch to position 3 and releasing relay |508. Y

When thesequence switch |509 reaches position 3 the key-set is ready to transmit the hundreds digit to the sender. In this position circuit A is open at the contacts of key |3|1. Circuit B is extended over the lower right contact of carn |405 through the windings of relay |5|| to ground at the upper back contact of relay |5|2. A branch of this circuit extends over the upper right contact of Vcam |405, inner right contact of key |3|1, left contacts of cam |42| to the lower winding of relay |5|| in shunt of the upper high resistance winding thereby creating a low resistance ground condition on circuit B. When the sender is ready to receive this digit When and completes circuits A, B and C, relay |5|| operates and locks to ground at its own lower front contact. Circuit C extends through resistance |4| 2, upper front contact of relay |5||, resistance |5|3 to ground over the lower contacts of cam |5|4. With sequence switch |500 in position 3 a circuit is closed from battery over the upper contacts of cam |4| windings of relay |4|4, lower right and upper left contacts of cam |4|5, left contact of key |3|1, upper right contact of cam |4|3 to ground over the lower left contact Aof cam |5|4. Relay |4|4 operates in this circuit and closes a shunt over its contact and the lower right contact of cam |401 around resistance |4|2, thereby transmitting low resistance ground over circuit C.

With sequence switch |500 in position 3 a circuit is prepared from battery over the left contacts of cam |509, through the winding of relay |5|2 to ground but relay |5|2 is prevented from operating by meansV of a shunt over its lower back contact and the normal contact of relay |5||. When relay |5|| operates in circuit B, as previously described, it opens this shunt and relay |5| 2 operates. As before, the registration of the hundreds digit in the sender causes the temporary opening of all three registering circuits and relay |5|| releases', closing a circuit from ground over its normal contact and the front contact of relay |5|2 to the upper right contact of cam |5||) and the winding of sequence switch magnet |500, advancing the sequence switch to position 4.

In position 4 circuit A extends over the lower right contact of cam |406, through the two windings of relay |408 to ground at the back contact of relay |508 creating a high resistance ground on circuit A. Circuit B extends over the upper left contact of cam |405, left contact of key |329, upper winding of relay |4|6, left contacts of cam |4|| to battery. With relays |408 and |4|6 operated circuit C extends over the upper contacts of cam |401, front contact of relay |4|6, upper contact of relay |408, resistance |410 to battery over the lower right and upper left contacts of cam |4| I, thereby creating a low resistance battery condition on circuit C. As before relay |408 operates relay |508 and, when the sender has completed the registration, is released to advance sequence switch |500 to position 5.

When the sender is ready for the next registration the three registering conductors are extended to the units register in the sender. In

the key control circuit, registering circuit A is extended over the upper right contact of cam |406, left contact of key |333 to battery over the left contacts of cam |4|1 and low resistance |4|8. Circuit B may be traced over the lower left contact of cam |50|, inner right contact of key |333, right contacts of cam |42|, lower winding of relay |5|| to ground at the back contact of relay |5|2. The normal circuit over the lower right contact of cam |405 to the two windings of relay |5|| is also closed. With relay |5|| operated, a circuit is closed from ground over the lower contacts of cam |5|4, resistance |5|3, upper front contact of relay |5|| through resistance |4|2 and the lower right contact of cam |401 to connect a high resistance ground to registering circuit C.

Relay |5| permits the operation of relay |5|2 as previously described and after the completion of the registration releases to advance sequence switch |500 to position 6. 

